As rotation transmission devices capable of selectively performing and stopping the transmission of the rotation of an input shaft to an output shaft, for example, rotation transmission devices as disclosed in Japanese Unexamined Patent Application Publication No. 2009-293654 (hereinafter, JP 2009-293654) and Japanese Unexamined Patent Application Publication No. 2009-008172 (hereinafter JP 2009-008172).
The rotation transmission device disclosed in JP 2009-293654 includes an outer ring, an inner member arranged inside of the outer ring, circumferentially opposed pairs of rollers provided between a cylindrical surface of the inner periphery of the outer ring and respective cam surfaces of the outer periphery of the inner member, spring members pressing the respective pairs of rollers such that the spaces between the respective pairs of rollers widen, and a roller retainer retaining the rollers.
The roller retainer is constituted by two split retainer portions supported so as to be rotatable relative to each other. The two split retainer portions separately support the pairs of rollers such that the spaces between the respective pairs of rollers change with the relative rotation of the two split retainer portions. Also, the two split retainer portions are movable between the engagement position in which the spaces between the respective pairs of rollers are widened so that the pairs of rollers are engaged with the cylindrical surface of the inner periphery of the outer ring and the respective cam surfaces of the outer periphery of the inner member, and the disengagement position in which the spaces between the respective pairs of rollers are narrowed so that the pairs of rollers are disengaged from the cylindrical surface of the inner periphery of the outer ring and the respective cam surfaces of the outer periphery of the inner member.
This rotation transmission device includes, as a means for moving the two split retainer portions from the engagement position to the disengagement position, an axially movably supported armature, a rotor axially opposed to the armature, an electromagnet configured to attract the armature to the rotor when the electromagnet is energized, and a ball ramp mechanism configured to convert the motion of the armature when attracted to the rotor into the movement of the two split retainer portions from the engagement position to the disengagement position.
The armature is biased away from the rotor by the spring force of the above spring members, pressing the respective pairs of rollers. Namely, the pressing force of the above spring members, which press the respective pairs of rollers such that the spaces between the respective pairs of rollers widen, is transmitted, as a circumferential force, to the two split retainer portions. This circumferential force is converted by the ball ramp mechanism into an axial force, and is transmitted to the armature, so that the spring force/load biasing the armature away from the rotor is applied to the armature.
While the electromagnet is de-energized, the rotation transmission device of JP 2009-293654 is in the engaged state in which rotation is transmitted between the outer ring and the inner member. Namely, while the electromagnet is de-energized, since the pairs of rollers are presses by the respective spring members such that the spaces between the respective pairs of rollers widen, the pairs of rollers are kept in engagement with the cylindrical surface of the inner periphery of the outer ring and the respective cam surfaces of the outer periphery of the inner member. When rotation is input to the outer ring or the inner member in this state, the rotation is transmitted between the outer ring and the inner member through the rollers.
On the other hand, while the electromagnet is energized, this rotation transmission device is in the disengaged state (idling state) in which rotation is not transmitted between the outer ring and the inner member. Namely, when the electromagnet is energized, the armature is attracted to the rotor, and due to this motion of the armature, since the two split portions rotate relative to each other such that the spaces between the respective pairs of rollers narrow, the rollers are disengaged from the outer ring and the inner member. If rotation is input to the outer ring or the inner member in this state, the rotation is not transmitted between the outer ring and the inner member.
The rotation transmission device of JP 2009-008172 includes an outer ring, an inner member arranged inside of the outer ring, pairs of rollers provided between a cylindrical surface of the inner periphery of the outer ring and respective cam surfaces of the outer periphery of the inner member, and a roller retainer retaining the rollers. The roller retainer are circumferentially movably supported between the engagement position in which the spaces between the pairs of rollers are engaged with the cylindrical surface of the inner periphery of the outer ring and the respective cam surfaces of the outer periphery of the inner member, and the disengagement position in which the pairs of rollers are disengaged from the cylindrical surface of the inner periphery of the outer ring and the respective cam surfaces of the outer periphery of the inner member. Also, the roller retainer is held in the disengagement position by the spring force of a switch spring.
This rotation transmission device includes, as a means for moving the roller retainer from the disengagement position to the engagement position, an axially movably supported armature, a rotor axially opposed to the armature, a spring member pressing the armature away from the rotor, an electromagnet configured to attract the armature to the rotor when the electromagnet is energized, and a friction clutch mechanism configured to convert the motion of the armature when attracted to the rotor into the movement of the roller retainer from the disengagement position to the engagement position.
While the electromagnet is de-energized, the rotation transmission device of JP 2009-008172 is in the disengaged state (idling state) in which rotation is not transmitted between the outer ring and the inner member. Namely, while the electromagnet is de-energized, since the roller retainer is held in the disengagement position by the switch spring, the rollers are disengaged from the outer ring and the inner member. If rotation is input to the outer ring or the inner member in this state, the rotation is not transmitted between the outer ring and the inner member.
On the other hand, while the electromagnet is energized, this rotation transmission device is in the engaged state in which rotation is transmitted between the outer ring and the inner member. Namely, when the electromagnet is energized, the armature is attracted to the rotor, and due to this motion of the armature, since the roller retainer moves to the engagement position from the disengagement position, the rollers are kept in engagement with the cylindrical surface of the inner periphery of the outer ring and the cam surfaces of the outer periphery of the inner member. When rotation is input to the outer ring or the inner member in this state, the rotation is transmitted between the outer ring and the inner member through the rollers.
In the rotation transmission devices described above, when the armature is attracted to the rotor by energizing the electromagnet, a collision sound arises between the armature and the rotor. Such a collision sound leads to a problem, especially, in the field of automobiles in which high silence is required nowadays (e.g., in the field of backup clutches used for steer-by-wire type steering devices).
In order to reduce the collision sound generated when an armature is attracted to a rotor, the inventors of the present application tried to add a rubber member between an armature and a rotor in a rotation transmission device as disclosed in JP 2009-293654, and performed an evaluation test on this arrangement in their company. As a result of this test, it turned out that if a rubber member is added between an armature and a rotor, the motion of the armature might be made stable.
Namely, when an electromagnet is energized, an armature receives not only the force attracting the armature to a rotor by the energized electromagnet, but also the forces of a rubber member and a spring member biasing the armature away from the rotor. If the force attracting the armature to the rotor is larger than the forces biasing the armature away from the rotor, the armature is attracted to the rotor.
The force attracting the armature to the rotor by the energized electromagnet changes with the distance between the armature and the rotor, i.e., increases as the armature approaches the rotor. Specifically, when the armature is relatively remote from the rotor, the attracting force slowly increases as the armature approaches the rotor, whereas when the armature is relatively close to the rotor, the attracting force rapidly increases as the armature approaches the rotor. Namely, the closer the armature is located to the rotor, the more sharply the armature tends to accelerate.
Therefore, if a rubber member is used of which the rubber compressing load (i.e., the force necessary for compressing the rubber member) is small, it is impossible to restrain the acceleration of the armature right before the armature is attracted to the rotor, and thus to effectively reduce a collision sound by the armature and the rotor. On the other hand, if a rubber member is used of which the rubber compressing load is large, it turned out that in the stage in which the armature moves toward to the rotor, the combination of the respective forces, which the armature receives from the spring member and the rubber annulus so as to be biased away from the rotor, might temporarily become larger than the force attracting the armature to the rotor by the energized electromagnet, so that the armature might not be attracted to the rotor.
In the rotation transmission device of JP 2009-008172, similarly, if a rubber member is added between the armature and the rotor so as to reduce a collision sound by the armature and the rotor, the motion of the armature might be made unstable.
It is an object of the present invention to provide a rotation transmission device in which a collision sound by an armature and a rotor is less likely to occur, and further the armature is stably attracted to the rotor.